Two years prior to his trial, Engarde dated his manager Celeste Inpax. Adrian Andrews, who would later became Engarde's manager, described them as being happy. However, he broke up with Inpax one day. Later, he learned that his rival Juan Corrida was planning to marry her. Knowing that it would hurt Corrida deeply, Engarde confessed to his fierce rival that he had dated her first. Corrida called off the marriage; heartbroken again, Celeste Inpax hanged herself, allegedly leaving a suicide note that was hidden by the man who found her body, Juan Corrida.

Stealing the show as the Nickel Samurai at the Hero of Heroes Grand Prix.

For the remaining years, the two men continued their rivalry with Engarde rising to the top of his acting career. Engarde gained a reputation for being "refreshing like a spring breeze", besting Corrida in popularity polls. This culminated in Engarde's starring role in The Nickel Samurai, which competed with Corrida's show Jammin' Ninja. Corrida, however, conspired with Andrews, who became Engarde's manager, to disclose the suicide note, which Corrida had actually forged, that would destroy that image.

During the Hero of Heroes Grand Prix at Gatewater Imperial Hotel, which the Nickel Samurai won, Corrida arranged a press conference, during which he would appear in the Nickel Samurai costume and reveal the false suicide note. Realizing that Corrida was a threat to his reputation, Engarde purchased spy cameras to keep close tabs on him and eventually hired a professional assassin named Shelly de Killer to kill him for the bear figurine that contained Inpax's suicide note. Engarde recorded the killing to use as a way to blackmail de Killer. De Killer posed as Engarde's butler and as a bellboy at the hotel where Corrida was murdered to ward off suspicion.

Engarde was arrested for Corrida's murder because of evidence planted by Andrews. In response, de Killer abducted Maya Fey to force defense attorney Phoenix Wright into getting an acquittal for Matt Engarde. At first, Wright did not suspect that Engarde was involved; Engarde said that he had killed no one, which was true and so did not reveal any Psyche-Locks. However, during his investigation, Wright discovered a spy camera planted in a giant stuffed bear at the crime scene (Corrida's room at the Gatewater Hotel), which he found had been purchased by Engarde.

Wright confronted Engarde at the detention center and accused him of hiring de Killer to assassinate Juan Corrida. When Wright figured out the truth, Engarde finally showed his true colors, flipping his hair back to reveal four scars on his right eye. He revealed his entire plan to Wright, and he told him that he placed his trust in absolutely no one, let alone assassins.

Forced to confess.

During the final trial, Engarde ordered de Killer, who had escaped from the police with his captive the night before, to bring the videotape containing the recording of the murder to him, instructing him not to view it himself. However, de Killer failed and left the tape, along with three other pieces of evidence, behind for Dick Gumshoe to take. Franziska von Karma eventually brought the tape to the trial. Wright informed de Killer of his client's plans of blackmail, which angered the assassin. He broke his contract with Engarde, releasing the hostage Maya Fey, and vowed to kill him. At this, with only one way out of facing the wrathful de Killer, Engarde broke down, ripping new scars into his face and repeating, "GUILTY!"

Engarde is notable for being one of only two clients of Wright's who was guilty of a crime for which he was arrested. His case gave Wright the only guilty verdict in his entire law career, while Wright earned the other client an acquittal. He was also one of only two clients not to be acquitted by Wright, the other being Zak Gramarye due to the latter's escape before a verdict could be given.

Engarde was a seemingly careless, weak-willed, and somewhat self-absorbed young man, with a liking for wine and motorcycles but no apparent control of his own life. He took every opportunity to use his wristwatch cell phone to ask his manager, Adrian Andrews, about even the most basic decisions. He was not a very tactful speaker, and had the habit of addressing people as "dude", calling Wright "Mister Lawyer dude". However, Engarde was also an infamous playboy who used his boyish charm and seemingly pleasant attitude to gain popularity with women. He justified his actions by calling it "just a game." When it came to rival Juan Corrida, he was known for being extremely competitive.

Engarde's seemingly harmless and flaky persona, however, was only a façade, designed to divert negative attention away from him so that no one would suspect him of any wrongdoing. In actuality, he was a cruel, cold, textbook sociopath, seeing other people as objects he could manipulate to further his own ends and then promptly discard. This difference in personality was so stark that Engarde even spoke of his "other self" as a separate person, as if he had some sort of identity disorder. Scheming and extremely paranoid, he trusted no one, but this ironically proved his undoing.

"Outorou" (王都楼) is a rough romanization of the English word "outlaw". It is also a reference to "ōtoro" (大とろ), a Japanese word for the fattiest portion of a bluefin tuna belly. This fish theme fits in with the Japanese name of Will Powers.

"Matt" is a diminutive of the given name "Matthew", which comes from the Hebrew for "Gift of God" (suiting Engarde's self-absorbed personality), but is also sometimes seen as an anglicisation of the Irish name "Mathúin", meaning "bear" (fitting Corrida's association with the animals). "Matt" itself is also the German word for "checkmate" and the Luxembourgish word for "moth". "Checkmate" suits the way Engarde treats other people like disposable pawns in a game of chess, and he could be seen as being as equally attracted to the "spotlight" of fame as moths are to a source of light.

"En garde" is a French phrase that means "on guard". It is usually associated with the sport of fencing. It is likely meant as a reference to his "on guard" nature, as he never trusts anyone, or it may be a reference to the "duel" between Corrida and himself. "Engarde" also fits with "Corrida", since they are both foreign words relating to fighting ("engarde" with fencing and "corrida" with bullfighting).

At the end of the Gyakuten Saiban film, a trial is shown with Wright as the defense attorney, Edgeworth holding the Jammin' Ninja's signature bright red guitar, a witness appearing to be Matt Engarde (albeit wearing a different outfit), and with a person appearing to be Adrian Andrews as the defendant.